1. Field of the Invention
The invention relates to a method for transmitting data in a radio communication system or a mobile transmitter and/or receiver station for such purpose.
2. Description of the Related Art
In mobile communication systems, such as, for example, GSM (Global System for Mobile Communications) or UMTS (Universal Mobile Telecommunications System), the transmitting power of the communication partner is optimized with respect to the quality of the connection. To this end, control mechanisms are used, which set the transmitting power so as to attain a desired bit error rate and/or a certain level of reception.
In ad hoc networks, also referred to as self-organizing networks, several network stations are able to create a radio connection between each other without a central transmitting device. The connection between two stations is made either direct or where the distance between them is greater, the connection is made via further stations of the same kind, which form relay stations for this connection. These self-organizing networks are, for example, local radio networks (WLANs: Wireless Local Area Networks) in accordance with the HiperLAN and IEEE 802.11 standards. Such networks are not only used in the usual Internet and telematics areas but also in the area of inter-vehicle communication, such as, for example, systems warning of dangers or cooperative driver assistance systems.
A particular advantage of ad hoc networks lies in their great mobility and flexibility. Radio connections can be created between stations wherever required and they are not dependent on permanently installed base stations or on a predetermined radio network plan. Thereby, connections from one station to a target station can be realized directly or by relay stations via a large number of possible paths. The great mobility of the individual stations that make up the ad hoc network, however, also implies that the environment conditions can change very quickly for a subscriber in an ad hoc network. If the power used when transmitting is too great, or if an outside station transmitting on the same resource moves into the receiving area of a receiving station, this results in increased interference on various connections and in a reduction in the quality of reception in the individual connections.
In HiperLAN 1 and 2 there are performance classes, which give the transmitting power intensity for a station for different situations. There are no performance classes in IEEE 802.11. Normally the mobile stations transmit using the maximum power provided for in the standard. Power regulation is not provided for.
What is problematic, especially with ad hoc networks, is a situation where two clusters each having one transmitting and one receiving station are moving towards each other. If the respective selection of the resources on the radio interface of the two clusters is made at a moment in time when there is as yet no knowledge of the other cluster, then there is a possibility that the transmitting stations of both clusters select exactly the same resource for their transmissions. In particular with clusters that are moving towards each other quickly, there is a danger that the receiving station of a clusters, as well as receive signals from its own assigned transmitting station, also receives signals from the other transmitting station of the other cluster. In this case, interference would occur, which in a bad case could prevent a reconstruction of the desired receive signal.
According to the IEEE 802.11 Standard, the influence of the mobility on the transmission efficiency can be compensated for by controlling the transmitting power and by adapting the error correction capacity. Disadvantageously, the maximum permitted transmitting power and the possibilities for adapting the error correction capacity are limited and, therefore, not sufficiently suited to compensate when the mobility is high.
Moreover, the use of power control mechanisms can even increase system instability within mobile ad hoc networks. As soon as the distance between the two clusters becomes less, the two transmitting stations would increase their own transmitting power to compensate for detected interference from the transmitting station of the other cluster. Consequently, the receiving stations measure increasing interference and prompt their own transmitting station to increase its transmitting power further. Disadvantageously the power control mechanisms currently used are not sufficiently powerful for such compensation.